This invention relates generally to an improved electrophotographic paper and more particularly to a bondlike copy paper which despite being coated has the general appearance, feel and handle of ordinary uncoated cockled bond paper.
Moreover, this invention relates to texturing of plain bond paper such as those in Xerox (TM) type machines, and also electrographic papers.
Known electrophotographic coated paper is comprised of a conductive base or substrate, ordinarily a treated paper, and a photoconductive layer bonded to and supported by the substrate. The photoconductive layer comprises a resinous substance having dispersed therein finely divided particles of photoconductive material, such as zinc oxide. Such papers are suitable for imaging in accordance with the well-known photoelectrostatic copying process and may be developed by using a pigmented thermoplastic powder that is attracted to the image areas and fixed to the imaging surface of the sheet of paper by heating, or developed by use of liquid toners in known fashion.
In general, conventional photoelectrostatic copy sheets do not look, feel, and handle like ordinary bond paper and for this reason have not enjoyed more widespread commercial success.
For instance, known photoelectrostatic copy papers of zinc oxide type have a smooth flat imaging surface tending to be glossy and thus reflect illumination in a mirrorlike fashion to produce glare. Such known copy papers are described and discussed in "Xerography and Related Processes," edited by John H. Dessauer and Harold E. Clark, The Focal Press, London and New York, 1965; also in Young, C. J. and Grieg, H. G., "RCA Review," 15, page 471 (1954). These known copy papers produce images that are somewhat difficult to read in certain orientations with respect to the source of light. Further, this smooth surface is also a poor medium on which to write with pen or pencil.
Known copy sheets suffer from a further disadvantage in that as a result of employing a dense, low bulk, supercalendered base paper which enhances the smoothness of the imaging surface, the copy sheets tend to be heavier than ordinary paper and feel limp.
Other potential base papers are those which do not have a flat surface, but are either cockled or embossed, presenting a rough, puckered appearance. Those found that such base papers give an uneven zinc oxide coating which leads to background toning problems. Further, in the preparation of conventional copy sheets, care has usually been taken to insure against producing a rough imaging surface sine it has heretofore been considered important to have maximum smoothness of this surface in order to avoid mechanical entrapment of the developer powder in the background or nonimaged areas of the sheet.
According to my invention the supporting base paper may or may not be pretreated for solvent holdout (and dispersant holdout, if intended for use with a liquid developer) and to provide conductivity. Of course, if the solvent holdout is not present, a certain amount of penetration by the photoconductive mixture into the paper is allowed which, in itself, helps improve the overall feel of the paper and makes the zinc oxide coating conform more closely to the fine texture of the paper. Whether the base paper chosen is pretreated or not, my process of cockling the electrophotographic coated paper after applying a suitable photoconductive coating will render the desired appearance and feel of typing bond paper, not previously achieved by other means. This texture may even be achieved by cockling or embossing single sheets after exposing and developing the finished electrophotographic paper.
In a conventional method of preparing copy sheets of the above-mentioned types, a resin material is dissolved in an organic solvent medium, principally toluene. Photoconductive particles of zinc oxide are then mixed with this liquid medium until a paintlike consistency is achieved. The mixture is then applied as a coating to a paper base and the solvent medium is evaporated, leaving a thin photoconductive layer bonded to the support surface of the base paper. The invention will demonstrate how my copy paper can give a better bondlike appearance by using applicable texturing techniques -- cockling by drying or embossing or the like -- after coating.